1. Field of the Invention
The invention pertains to the field of semiconductor devices. More particularly, the invention pertains to optoelectronic devices, such as laser diodes, light-emitting diodes and semiconductor optical amplifiers.
2. Description of Related Art
Light-emitting devices are broadly applied in modem optical storage, material processing, display and lighting systems. These devices usually utilize directional light extraction from the device either perpendicular to the surface or perpendicular to the edge facet, with power concentration is a certain angle. In a number of applications it is very desirable that the optical density per unit angle is as high as possible. Unfortunately, standard light emitting devices do not solve this problem. In light-emitting diodes the active media used in devices does not provide any angle selectivity. In edge-emitting lasers, to achieve sufficient modal gain for lasing, the active media is introduced into a narrow waveguide layer. Self-diffraction of the light at a narrow waveguide aperture at the laser facet may cause a significant broadening of the beam once it is exiting the crystal. Increasing thickness of the waveguide causes multimode operation with multiple emission lobes and, also, the threshold current density may be trongly increased. Another disadvantage of the conventional devices is the fact that their emission spectrum is broad, while most of the applications require wavelength-stabilized operation.